Tooth bioengineering is of great interest, because dental decay and tooth loss constitute an important public health issue. Additionally, tooth anomalies are common in many craniofacial syndromes, and the easy accessibility of the oral cavity makes teeth an excellent test case for organ replacement. A thorough understanding of the molecular processes that drive tooth renewal and regeneration will be crucial to efforts to build new teeth. We are using the mouse incisor as a model for understanding the mechanisms that underlie the ability of stem cells to contribute to renewal of dental tissues, because it grows continuously due to the presence of adult stem cells. In this application, we propose to learn about the role of transcriptional control of stem cell-driven tooth renewal in the mouse incisor by focusing on how Bmi1 regulates this process. Bmi1 is a Polycomb Group (PcG) protein that is required for stem cell self-renewal in multiple tissues. The experiments proposed in the application will first identify which differentiated cell types in the incisor arise from Bmi1- expressing stem cells using genetic lineage tracing approaches. Next, we will explore the functional role of Bmi1 in incisor stem cell self-renewal and differentiation in vivo and in vitro. Finally, we will identify genetic targets of Bmi1 and determine their function in dental stem cells. These studies will advance our understanding of how nature normally uses stem cells in dental regeneration. Such information will inform future efforts aimed at stem cell-based tooth bioengineering.